Field installed transmitter devices have been widely employed in process control situations to provide process variable information to control and/or data acquisition devices. Unlike laboratory measurement instrumentation, field devices are constructed using sealed protective enclosures to withstand adverse environmental conditions in manufacturing facilities, chemical processing plants, oil refineries and the like, in which the device may be subjected to extreme temperatures and humidity. Such devices are typically employed in distributed control systems for sensing temperature, fluid pressure, flow, and other variables used to control an ongoing process and are generally connected to other control equipment by a 4-20 mA control loop from which the transmitter derives its power and through which the sensed process variable is provided to the control system. Loop-powered transmitters are widely available for sensing various process variables, with the transmitter generally being configured to vary the loop current from 4 mA to 20 mA according to the measured process variable (e.g., with 0% of the process variable range being represented by 4 mA and 100% corresponding to 20 mA). Other transmitters offer digital communications according to standard protocols such as HART, etc. by which the transmitter can send and receive data, commands, and other information via the control loop.
Many chemical processes involve storage or transport of fluids in or through pipes, tanks and other structures, wherein these structures may corrode overtime due to contact with the transported or stored fluids. In these situations, it is desirable to ascertain the amount and rate of such corrosion to allow informed evaluation of the structural integrity for maintenance purposes and also to identify undesired or unexpected corrosivity levels in the fluids themselves, where the corrosion data may be used to apply remedial measures such as inhibitor injection and/or to ascertain and optimize the efficiency of such remedial measures. Other corrosion measurement applications include corrosion of structures exposed to non-fluids, such as corrosion of steel in concrete, wherein corrosion-causing materials generally, whether solid, liquid, or gaseous are referred to as electrolytes. However, it is often impractical to perform corrosion measurement using elaborate and expensive laboratory grade instrumentation and measurement systems due to the nature of most chemical processing environments and the size and location of pipelines and fluid holding tanks. In particular, such expensive systems are not adaptable to online measurement of pipeline or storage tank corrosion conditions in real time. Moreover, online measurement devices must be able to operate on very low power budgets, such as obtainable from a standard 4-20 mA control loop or from battery power. Field corrosion transmitters have recently been introduced to provide corrosion measurement capabilities for these applications. However, conventional field corrosion transmitters have thus far been unable to provide requisite levels of corrosion measurement accuracy and adaptability to measuring corrosion with respect to a wide variety of structure materials, transported fluid types, and temperatures whereby a need exists for improved field transmitters for measuring one or more corrosion related values.